1. Field of the Invention
The present invention relates to an object grasping system for automatic devices or artificial hands, and more particularly concerned with such a system wherein ideal variable-speed grasping motion is performed by mechanical fingers.
2. Description of the Prior Art
The great development of automatic devices such as industrial robots and artificial hands has resulted from various attempts to embody more reliable performance in these devices. It is very well known that the function of the automatic devices can be improved by the aid of highly efficient computers. In fact computer controlled automatic devices accurately guide working components such as a mechanical arm or hand system in their action to cause mechanical fingers to approach and properly hold an object in the required manner. Some of the latest developments are characterized by close similarity of operation to the human hand in which the mechanical hands dexterously handle objects. Among various other proposed devices, one type of fairly interesting which is so designed that the mechanical fingers of the system are first activated to approach the object at a high speed, and then movement of the mechanical fingers is automatically decreased in speed so that the fingers can grasp the object at a lower speed. This type of device has a particularly ideal feature in that the fingers approach the object at a high speed so as to save operation time, then in order to get a firm grasp of the object at a suitably lower speed with increased moment on the surface of the object, the movement of the fingers is caused to decrease in speed. There are various devices known as means for causing the mechanical hand system to operate at decreasing speed. Conventionally, these means have involved use of variable speed motors. However, the known mechanical hand systems utilizing variable speed motors as means for operating the mechanical hand system at changing speed require complex control systems, and have resulted in greater mechanical complications. As an alternative means, it is possible to use a mechanical hand system design composed of link mechanism wherein a mechanical link construction is so designed to achieve the effect of approaching the object with fingers at a high speed and actually grasping it at decreased speed and with increased moment upon the object. It is, however, not difficult to see that this mechanism also would necessarily be of complex design and require precision control means in establishing the desired performance.
Thus, although prior art mechanical hand systems having control means for attaining the desired mechanical functions have been developed to a fairly high degree of reliability, they are found to be undesirable in view of their complexity and the resulting large weight and size. In many applications, such as in artificial hands where light weight and small size are essential, this proves to be a great disadvantage. Furthermore, most of these mechanical hand systems of highly complicated design are prone to mechanical failure and increased maintenance problems because of the large number of components from which they are composed. Eventually, they have come to be regarded practically as unacceptable.